The luminosity function of white dwarfs

A variety of new data - trigonometric parallaxes, optical colors, and spectrophotometry - are presented for a sample of mostly cool white dwarfs having large proper motions. These and existing data from the literature are used to derive an empirical luminosity function for cool white dwarfs using the 1/Vmax method. The results show that a downturn occurs in the distribution of cool degenerate stars near log (L/L_sun;) ≡ -4.4. The reality of this deficiency is supported by the results of other kinds of investigations. The indicated local space density of observed degenerate dwarfs is 0.003 stars pc-3, which corresponds to ≡1% of the dynamical mass density in the solar neighborhood. The downturn at the faint end is probably caused by the near-equality of the cooling times of the lowest luminosity observed degenerates to the age of the Galactic disk. The latter is indicated to be in the (7 - 10)×109yr range.